This invention relates generally to golf equipment and, in particular, to golf club heads.
As is well known to golf manufacturers and many golfers, the “sweet spot” of a golf club head is a point on the front face of the club head at which a line drawn normal to the front face passes through the center of gravity of the golf club head. If a golfer swings a golf club so that the club head impacts a golf ball at the sweet spot, few if any harmonic vibrations are excited within the golf club head and shaft. Consequently, the maximum amount of energy from the golfer's swing is available for momentum transfer to the golf ball. Conversely, if the golfer swings the golf club so that the club head impacts the golf ball away from the sweet spot, the impact frequently excites various torsional and bending oscillations. Such a mis-hit has two deleterious consequences. The harmonic oscillations are felt as unpleasant vibrations transmitted to the golfer's hands and the energy lost through the harmonic oscillations is not available for momentum transfer to the ball and thus results in a shorter distance of travel for the golf ball for the same swing speed. This effect is compounded by the fact that in many cases the sweet spot of the front face is at or near the point of the front face with the highest compliance and therefore, the highest effective coefficient of restitution. Thus, a golf ball hit at the sweet spot will travel substantially further than a golf ball hit at a point on the front face away from the sweet spot. To counteract this effect, it would be advantageous to provide a golf club head having a variable resiliency across the front face.
U.S. Pat. No. 5,807,190 to Krumme, et al. discloses a club head in which the face insert is composed of many small rods arranged in a closely packed array. According to the Krumme patent, use of individual rod segments to form the front face allows the properties of the front face to vary in any pattern over the impact area, simply by varying the materials out of which the individual rods are made. Use of multiple materials within the array of rods could render a front face having the desired variable resiliency. Such use of multiple materials would, however, render the club non-conforming, for Rule 5(b) of Appendix II of the United States Golf Association requires that the whole of the impact area of a club head be of the same material. Accordingly, what is needed is a golf club head in which the resiliency of the front face may be varied across the front face without varying the rod material.